> what is the value of enabling mccs ?
> 
> additionally it seems to depend on c++ compiler, so more configuration
> on the port might be need (COMPILER variable for example).

mccs has been enabled by default since opam 2.2.0 and already requires a 
C++ compiler. See: https://github.com/ocaml/opam/pull/5527
Before opam 2.2 it was enabled if a C++ compiler was present (which 
should have been the case for OpenBSD). All of the other solvers were 
basically useless so in turn opam would become unusable on the rare 
platforms where C and C++ compilers are distributed separately.

So it really doesn't do anything to add it, but i've added it because i 
felt like being explicit was nice for future versions where it might be 
phased out. See: https://github.com/ocaml/opam/pull/6586

If you prefer to remove it, i don't mind at all, it's just for the sake 
of explicitness.

Many thanks,
Kate